The present invention generally relates to an implantable cardiac stimulation device. The present invention more particularly relates to such a device which includes a system for and implements a method of automatically conducting a non-invasive programmed stimulation (NIPS) procedure for inducing a tachyarrhythmia of a heart to permit the performance of electrophysiological studies.
Frequently, a clinician must perform electrophysiological studies in patients having implanted permanent pacemakers or cardioverters/defibrillators to determine accurately the patient""s pathological condition, cardiovascular characteristics and other information needed in order to prescribe a particular therapeutic treatment for the patient. Such studies often require the inducement of a tachyarrhythmia of the heart such as ventricular tachycardia.
Originally, these studies were invasive because they required the surgical insertion of instruments such as temporary intracardiac pacing catheters into the patient. Thus, these studies were accompanied by some risk and preferably were performed in hospitals. Therefore, these studies were not only expensive, but also time consuming and caused patient anxiety.
In order to avoid medical risks to the patient and hospitalization, non-invasive programmed stimulation (NIPS) procedures have been developed to permit the electrophysiological studies to be performed in a physician""s office during routine follow-up visits.
These procedures utilize the implanted cardiac stimulation device and an external programmer. By virtue of the presence of a permanent pacing/defibrillation lead associated with the implanted cardiac stimulation device, the need for placement of a temporary intracardiac pacing catheter is eliminated. Typically, NIPS procedures consist generally of the application of premature electrical pulses at precise intervals to the myocardium of the patient""s heart by the implanted cardiac stimulation device and its associated lead or leads. The implanted device applies the stimulation pulses under commands from the external programmer which is manually controlled by the clinician. Prior to the procedure, the clinician manually defines the intervals between the successive stimulation pulses on the programmer. After the implanted device applies the succession of stimulation pulses to the heart, the clinician then, on the programmer, manually observes results such as tachyarrhythmia induction or lack of capture by the stimulation pulses. Thereafter, the clinician alters the stimulation pulse intervals and causes the programmer to initiate another application of the successive stimulation pulses to the patient""s heart by the implanted cardiac stimulation device. As a result, NIPS studies, as currently constituted, are tedious to administer, consume considerable time, and lead to considerable cost to the electrophysiology laboratory.
The present invention provides a system and method for use in an implantable cardiac stimulation device that automatically induces a tachyarrhythmia of a heart to permit the performance of an electrophysiological test of the heart. In accordance with the present invention, the system and method permits the implantable cardiac stimulation device to perform a NIPS procedure automatically once initial parameters are established in the device by an external programmer under control of a clinician.
In accordance with the present invention, a NIPS protocol is stored in a memory within the implantable cardiac stimulation device. A processor accesses the NIPS protocol stored in the memory to control a pulse generator that repeatedly delivers groups of pacing pulses to a chamber of the heart. The pacing pulses are separated in time by pacing or interpulse intervals to overdrive pace the patient""s heart. After each group of pacing pulses is delivered to the heart, the processor varies the pacing intervals according to the NIPS protocol prior to reinitiating the delivery of the next group of stimulation pulses. The processor terminates the delivery of the stimulation pulses if it detects the tachyarrhythmia of the heart after a group of stimulation pulses have been delivered to the heart.
In accordance with a further aspect of the present invention, the processor, in accordance with the NIPS protocol, determines capture of the heart by each delivered stimulation pulse and terminates the delivery of the stimulation pulses to the heart by the pulse generator when a predetermined number of successive pacing pulses fail to capture the heart. In accordance with a still further aspect of the present invention, the processor requires a minimum pacing interval to determine capture of the heart by a stimulation pulse. In accordance with the NIPS protocol, the processor terminates the delivery of the stimulation pulses to the heart when a pacing interval falls below the minimum pacing interval.
In accordance with still further aspects of the present invention, each group of stimulation pulses includes a first set of pulses employed to capture the heart at an overdrive pacing rate and a second set of pulses to induce the tachyarrhythmia. The processor, in accordance with the NIPS protocol, varies the pacing intervals of the second set of pacing pulses between the application of the groups of stimulation pulses.
In accordance with still further particular aspects of the present invention, the second set of pacing pulses includes a last pulse and a second to the last pulse and the processor decrements the pacing interval between the last pulse and the second to the last pulse responsive to the last pulse capturing the heart in accordance with the NIPS protocol. Further, the second set of pacing pulses further includes a third to the last pulse. The processor, in accordance with the NIPS protocol, decrements the pacing interval between the second to the last pulse and the third to the last pulse and resets the pacing interval between the last pulse and the second to the last pulse to an initial interval responsive to the last pulse failing to capture the heart.
The application of the successive groups of pacing pulses is automatically continued with intergroup pacing interval adjustment until the tachyarrhythmia is detected by the processor. The procedure may further be terminated if manually terminated by the clinician, if a predetermined number of pacing pulses fail to capture the heart, or if a pacing interval falls below the minimum interval required by the processor to determine capture of the heart.